1. Field of the Invention
This invention relates to light-sensitive devices, and more particularly, to a focusing and color-filtering structure for use in a semiconductor light-sensitive device, such as a CMOS (complementary metal-oxide semiconductor) light-sensitive device and a method of fabricating the same.
2. Description of Related Art
A digital camera, or a PC (personal computer) camera, is a digital photographic apparatus that can produce photographed images directly in digital form instead of on traditional films, thus allowing immediate computer processing of the photographed images. A conventional digital camera typically includes an array of light-sensitive cells, such as CMOS (complementary metal-oxide semiconductor) light-sensitive diodes, which can convert the light incident thereon into analog electrical signals that can be further converted into digital form. These CMOS light-sensitive diodes are formed on a semiconductor substrate. Further, a focusing and color-filtering structure is formed over the CMOS light-sensitive diodes for focusing the incident light onto the corresponding light-sensitive diodes and also for separating the incident light into the three primary components, i.e., red (R), green (G), and blue (B) components prior to the light being detected by the light-sensitive diodes.
A conventional focusing and color-filtering structure for a CMOS light-sensitive device is illustratively depicted in the following with reference to FIGS. 1A-1B.
As shown in FIG. 1A, the CMOS light-sensitive device is constructed on a semiconductor substrate 10. A passivation layer 12 is formed over the substrate 10. Next, a plurality of color-filter layers 14 are formed over the passivation layer 12, each of the color-filter layers 14 consisting of a red-filter region (not shown), a green-filter region (not shown), and a blue-filter region (not shown), which are formed, for example, from acrylic materials of the respective color-filtering qualities. A planarization layer 16 is then deposited over the color-filter layers 14.
It is illustratively shown in FIG. 1A that the part of the planarization layer 16 that is deposited over the area where the color-filter layers 14 are located (hereinafter referred to as the filter area) and the part of the planarization layer 16 that is deposited over the area beyond the filter area (hereinafter referred to as the non-filter area) would have uneven thicknesses, resulting in a slope (as indicated by the reference numeral 18 in FIG. 1A) at the border between the filter area and the non-filter area. The forming of this slope 18 would cause some undesired drawbacks to the focusing and color-filtering structure, which will be described later.
Referring next to FIG. 1B, in the subsequent step, an array of microlenses 19 are formed over the planarization layer 16, with each of the microlenses 19 being aligned with one of the color-filter layers 14. The microlenses 19 are each used to focus the light incident thereon through the color-filter layers 14 onto the corresponding one of the light-sensitive diodes (not shown) in the substrate 10. This completes the fabrication of the CMOS light-sensitive device. The microlenses 19, the planarization layer 16, and the color-filter layers 14 are in combination referred to as a focusing and color-filtering structure for the CMOS light-sensitive device.
One drawback to the foregoing focusing and color-filtering structure, however, is that some of the microlenses 19 that are disposed on the slope 18 will have their optical axis slanted and thus misaligned with their corresponding light-sensitive diodes, thus resulting in a shift in the focused point. Moreover, since those of the microlenses 19 on the slope 18 are somewhat lower in position than those of the microlenses 19 that are not, the photographed image can be defocused, thus resulting in a blurred image. Still moreover since those of the microlenses 19 on the slope 18 are somewhat inclined sidewards, the ambient scattering light from the side can easily enter into these microlenses 19 on the slope 18 thus resulting in an undesired reception of unwanted light that would further degrade the quality of the photographed image.